The present invention relates to a new process for preparing ethyl3-(2,5, 6-trihalopyridin-3-yl)-3-oxopropionate (hereinafter xe2x80x9cETPOxe2x80x9d) which is usable as an intermediate of a quinolinic antibiotic. More particularly, the present invention relates to a new process for preparing ETPO from 2,5,6-trihalo-3-cyanopyridine (hereinafter xe2x80x9cTHCPxe2x80x9d) using a transition metal and ethyl haloacetate.
Ethyl 3-(2,5,6-trihalopyridin-3-yl)-3-oxopropionate which is usable as an intermediate of a quinolinic antibiotic is represented as the following formula: 
where X is a halogen atom such as F, Cl, Br or I.
It has been known a method of synthesizing ETPO in Japanese Patent Pulication Number 3-74231 published Nov. 26, 1991. The method of the Japanese Patent is to prepare ETPO from THCP through 4 steps process of hydration, chlorination, alkylation and dealkoxycarbonylation. The reaction scheme are shown as follow: 
The method of ETPO above according to the Japanese Patent has a lower yield in total such as 13%, because the method is carried out through 4 steps. Furthermore, the method is not economical in terms of the cost of preparation. In particular, the method is not practical, because the yield at the last step of dealkoxycarbonylation is very low and the method is not reproducible.
In order to overcome the disadvantages of the method of the Japanese Patent, Pfizer Inc. developed in 1997 a new method using ethyl acetoacetate as alkylation agent instead of diethyl malonate that had been used in the Japanese Patent. The reaction scheme of the method by Pfizer Inc. is represented as follow: 
However, the method by Pfizer Inc. failed to increase the total yield, which turns out 14% approximately.
As discussed above, both the method of the Japanese Patent and the method of Pfizer Inc. failed to increase the total yield in the preparation of ETPO. The preparation of ETPO in a low total yield means that ETPO cannot be prepared due to the high cost.
The present inventors have developed a new process for preparing ETPO from THCP in one step process using a transition metal and ethyl haloacetate, which can prepare ETPO having higher yield and purity compared to the ETPOs synthesized by a conventional method.
A feature of the present invention provides a new method of preparing ETPO from THCP in one step process using a transition metal and ethyl haloacetate.
Another feature of the present invention provides a method of preparing ETPO from THCP, the yield after recrystallization being about 80% or more.
A further feature of the present invention provides a method of preparing ETPO from THCP, the purity after recrystallization being about 97% or more.
A further feature of the present invention provides a method of preparing ETPO from THCP, which is economical in cost of preparation and has a good productivity by preparing ETPO having a yield of about 80% or more and a purity of about 97% or more after recrystallization.
Other objects and advantages of this invention will be apparent from the ensuing disclosure and appended claims.
The new process for preparing ethyl 3-(2,5,6-trihalopyridin-3-yl)-3-oxopropionate from 2,5,6-trihalo-3-cyanopyridine in accordance with the present invention comprises reacting 2,5,6-trihalo-3-cyanopyridine with ethyl haloacetate at the presence of a transition metal in powder in anhydrous solvent, and treating the resulting solution with HCl.
In particular, the new process for preparing ETPO from THCP comprises heating 2,5,6-trihalo-3-cyanopyridine and a transition metal in powder in anhydrous solvent to the boiling point, reacting 2,5,6-trihalo-3-cyanopyridine with ethyl haloacetate by adding ethyl haloacetate dropwise to the resulting solution, cooling the resulting solution to about 10xc2x0 C., adding concentrated HCl and distilled water to the resulting solution during agitation thereof, and filtering the product.
The ETPO obtained in accordance with the present invention has a yield of about 80% or more and a purity of about 97% or more after recrystallization.
According to the present invention, ethyl 3-(2,5,6-trihalopyridin-3-yl)-3-oxopropionate is directly prepared in one step process compared to the conventional processes from the starting material of 2,5,6-trihalo-3-cyanopyridine. First, THCP is reacted with ethyl haloacetate at the presence of a transition metal in powder in anhydrous solvent, and the resulting solution is treated with concentrated HCl solution. Then the resulting solution is filtered and the filtrates are recrystallized to produce ETPO having high purity. The reaction for preparation of ETPO in accordance with the present invention is represented as follow: 
where X is a halogen atom and M is a transition metal.
More particularly, a transition metal in powder and THCP are added to anhydrous solvent and the resulting solution is heated to the boiling point. Particular preferred examples of anhydrous solvent according to the present invention include anhydrous tetrahydrofuran (THF) and anhydrous diethyl ether. Particular preferred examples of transition metal according to the present invention include Mg Zn, Sn, Pb, Cu, Ag, Ni and Co. The transition metal in the state of powder can be preferably used. The transition metal powder is preferably activated at 0-30xc2x0 C. Before heating the resulting solution, the activated transition metal powder and THCP are under reduced pressure or vacuum to evaporate moisture and solvent, and then nitrogen gas is filled. To the reactor is anhydrous solvent added and the resulting solution is heated to the boiling point.
To the heated solution is ethyl haloacetate dropwise added to react THCP with ethyl haloacetate by adding ethyl haloacetate. Particular preferred examples of ethyl haloacetate include ethyl chloroacetate, ethyl bromoacetate, and ethyl iodoacetate. The ethyl haloacetate is dropwise added over about 1-3hours. After the ethyl haloacetate is dropwise added, the resulting solution is fluxed for about 30 minutes to about 1 hour to react further THCP with ethyl haloacetate.
The resulting solution is cooled to about 10xc2x0 C., and concentrated HCl and distilled water are added to the cooled solution during agitation. The resulting solution is agitated for about 2 hours.
The agitated product is filtered to obtain unpurified ETPO in a yield of about 90% or more. The filtrate is washed within short time by putting into solvent. Cool ethanol, THF or ethyl acetate is preferably used as the solvent. The washed filtrate is put into solvent and heated to 60xc2x0 C. to dissolve. The solvent is distilled and the product is quenched to obtain ETPO through recrystallization. The reflux, cooling, agitation, filtration and recrystallization above according to the present invention are easily carried out by an ordinary person in the art to which the present invention pertains. During the recrystallization, the solvent used to wash the filtrate is preferably collected and recycled with the solvent of other batches to obtain additional ETPO.
The unpurified ETPO is recrystallized using solvent to obtain purified ETPO having a high yield of about 80% or more in a yield of about 90% or more.
The invention may be better understood by the reference to the following examples which are intended for the purpose of illustration and are not to be construed as in any way limiting the scope of the present invention, which is defined in the claims appended hereto. In the following examples, all parts and percentage are by weight unless otherwise indicated.